Oligonucleotides containing the 5' termini of adenovirus 2 mRNA are selectively retained on columns of dihydroxyboryl cellulose. When total late adenovirus 2 mRNA was treated with RNAase T1, a single 5' terminal oligonucleotide was isolated, although in several states of methylation. This oligonucleotide has the general structure m7G5'ppp5' AmCmU(C4,U3)G. Since at least twelve individual species of mRNA must be present late after infection, this finding was unexpected and its significance is discussed.